Solvent types hydrogen-bond acceptor

The choice of solvent is of particular importance. First, it has to be chosen such that the solubility is in a suitable range for the selected type of crystallization experiment (reasonably high solubility for cooling experiments, very low solubility in solvents used for precipitation, etc.). Second, it is important to use solvents with diverse physical properties in order to explore the whole parameter space of possible environments. In addition to molecular solvent-solute interactions, bulk properties of solvents such as viscosity may play a role. Gu et al. [19] examined 96 solvents in terms of 8 relevant solvent properties hydrogen bond acceptor propensity, hydrogen bond donor propensity, polarity/dipolarity, dipole moment, dielectric constant, viscosity, surface tension, and cohesive energy density (calculated from the heat of vaporization). Based on all 8 properties, the 96 solvents were sorted into 15 groups... 

In contrast to inorganic molten salts, the fluidity of ionic hquids at room temperature permits their use as solvents for chemical reactions. Electrostatic properties and charge mobility in ionic hquids can play a distinctive role in chemical reactivity, as compared with neutral solvents. In particular, hydrogen and proton transfer reactions are likely to be sensitive to an ionic environment due to the hydrogen-bond acceptor ability of the anions. Such type of reactions are fundamental in acid-based chemistry and proton transport in solution. 

The following treatment is based on the use of three different scales [i.e., (S), g2(S), and g3(S)] which have been determined empirically the polarity scale 7T, the a scale of solvent hydrogen bond donor (HBD) acidities (71), and the /3 scale of solvent hydrogen bond acceptor (HBA) basicities (72). To avoid possible pitfalls resulting from experimental errors or from specific solvent effects, the solvatochromic parameters have been arrived at by averaging multiple, s determined for each solvent with a variety of different indicators. Quite generally, the purpose of this study is the systematic correlation of solvent effects on diverse properties and reactivity parameters, XYZ, by means of expressions of the type. 

Hydrogen bond type, hydrogen bond donor/acceptor ability P poor, M medium, S strong + favorable as solvent for imprinting, -less favorable as solvent for imprinting. 

Taft and coworkers described the formulation of three scales of solvent properties which were used to unravel and rationalize solvent effects on many types of physico-chemical properties. A tt scale of polarity/polarizabilities describes the solvent s ability to stabilize a charge or a dipole by virtue of its dielectric effect. The n values have been shown to be generally proportional to molecular dipole moments. The a scale of hydrogen bond donor acidities provides a measure of the solvent s ability to donate a proton. The jS scale of hydrogen bond acceptor basicities quantifies the solvent s ability to donate an electron pair (accept a proton). 

Furthermore, it is often possible to extract from the structural analysis of solid solvates a significant information on solvation patterns and their relation to induced structural polymorphism. An interesting illustration has been provided by crystal structure determinations of solvated 2,4-dichloro-5-carboxy-benzsulfonimide (5)35). This compound contains a large number of polar functions and potential donors and acceptors of hydrogen bonds and appears to have only a few conformational degrees of freedom associated with soft modes of torsional isomerism. It co-crystallizes with a variety of solvents in different structural forms. The observed modes of crystallization and molecular conformation of the host compound were found to be primarily dependent on the nature of the solvent environment. Thus, from protic media such as water and wet acetic acid layered structures were formed which resemble intercalation type compounds. 

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